Factor out checkerboard function in gm and sampleapp into tools.

Review URL: https://codereview.chromium.org/834303005

15 files changed, 125 insertions, 194 deletions

diff --git a/gm/colorwheel.cpp b/gm/colorwheel.cpp
index f74eaf6a98..8cf94646e5 100644
--- a/gm/colorwheel.cpp
+++ b/gm/colorwheel.cpp
@@ -5,29 +5,12 @@
  * found in the LICENSE file.
  */
 
+#include "Checkerboard.h"
 #include "Resources.h"
 #include "SkData.h"
 #include "gm.h"
 #include "sk_tool_utils.h"
 
-static void checkerboard(
-        SkCanvas* canvas, int w, int h, int size, SkColor c1, SkColor c2) {
-    SkAutoCanvasRestore autoCanvasRestore(canvas, true);
-    canvas->clipRect(SkRect::MakeWH(SkIntToScalar(w), SkIntToScalar(h)));
-    canvas->drawColor(c1);
-    SkPaint paint;
-    paint.setColor(c2);
-    SkScalar s = SkIntToScalar(size);
-    for (int y = 0; y < h; y += size) {
-        SkScalar ty = SkIntToScalar(y);
-        bool oddRow = (y % (2 * size)) != 0;
-        for (int x = oddRow ? size : 0; x < w; x += (2 * size)) {
-            SkScalar tx = SkIntToScalar(x);
-            canvas->drawRect(SkRect::MakeXYWH(tx, ty, s, s), paint);
-        }
-    }
-}
-
 static void draw_bitmap(SkCanvas* canvas, const char* resource, int x, int y) {
     SkBitmap bitmap;
     if (GetResourceAsBitmap(resource, &bitmap)) {
@@ -48,8 +31,7 @@ static void draw_bitmap(SkCanvas* canvas, const char* resource, int x, int y) {
   background and compression artifacts.
  */
 DEF_SIMPLE_GM(colorwheel, canvas, 256, 256) {
-    canvas->clear(SK_ColorWHITE);
-    checkerboard(canvas, 256, 556, 8, 0xFF999999, 0xFF666666);
+    sk_tools::DrawCheckerboard(canvas);
     draw_bitmap(canvas, "color_wheel.png", 0, 0);  // top left
     draw_bitmap(canvas, "color_wheel.gif", 128, 0);  // top right
     draw_bitmap(canvas, "color_wheel.webp", 0, 128);  // bottom left
diff --git a/gm/displacement.cpp b/gm/displacement.cpp
index dddf8a53c4..f35d5acd3f 100644
--- a/gm/displacement.cpp
+++ b/gm/displacement.cpp
@@ -5,9 +5,10 @@
  * found in the LICENSE file.
  */
 
-#include "gm.h"
-#include "SkDisplacementMapEffect.h"
+#include "Checkerboard.h"
 #include "SkBitmapSource.h"
+#include "SkDisplacementMapEffect.h"
+#include "gm.h"
 
 namespace skiagm {
 
@@ -47,22 +48,7 @@ protected:
     void make_checkerboard(SkBitmap* bitmap, int w, int h) {
         bitmap->allocN32Pixels(w, h);
         SkCanvas canvas(*bitmap);
-        canvas.clear(0x00000000);
-        SkPaint darkPaint;
-        darkPaint.setColor(0xFF804020);
-        SkPaint lightPaint;
-        lightPaint.setColor(0xFF244484);
-        for (int y = 0; y < h; y += 16) {
-          for (int x = 0; x < w; x += 16) {
-            canvas.save();
-            canvas.translate(SkIntToScalar(x), SkIntToScalar(y));
-            canvas.drawRect(SkRect::MakeXYWH(0, 0, 8, 8), darkPaint);
-            canvas.drawRect(SkRect::MakeXYWH(8, 0, 8, 8), lightPaint);
-            canvas.drawRect(SkRect::MakeXYWH(0, 8, 8, 8), lightPaint);
-            canvas.drawRect(SkRect::MakeXYWH(8, 8, 8, 8), darkPaint);
-            canvas.restore();
-          }
-        }
+        sk_tools::DrawCheckerboard(&canvas, 0xFF244484, 0xFF804020, 8);
     }
 
     virtual SkISize onISize() {
diff --git a/gm/imagefiltersclipped.cpp b/gm/imagefiltersclipped.cpp
index beb2e0977a..259342cc27 100644
--- a/gm/imagefiltersclipped.cpp
+++ b/gm/imagefiltersclipped.cpp
@@ -5,19 +5,20 @@
  * found in the LICENSE file.
  */
 
-#include "gm.h"
-#include "SkColor.h"
+#include "Checkerboard.h"
 #include "SkBitmapSource.h"
 #include "SkBlurImageFilter.h"
+#include "SkColor.h"
 #include "SkDisplacementMapEffect.h"
 #include "SkDropShadowImageFilter.h"
 #include "SkGradientShader.h"
+#include "SkMatrixImageFilter.h"
 #include "SkMorphologyImageFilter.h"
 #include "SkOffsetImageFilter.h"
 #include "SkPerlinNoiseShader.h"
 #include "SkRectShaderImageFilter.h"
-#include "SkMatrixImageFilter.h"
 #include "SkScalar.h"
+#include "gm.h"
 
 #define RESIZE_FACTOR_X SkIntToScalar(2)
 #define RESIZE_FACTOR_Y SkIntToScalar(5)
@@ -40,27 +41,6 @@ protected:
         return SkISize::Make(860, 500);
     }
 
-    void make_checkerboard() {
-        fCheckerboard.allocN32Pixels(64, 64);
-        SkCanvas canvas(fCheckerboard);
-        canvas.clear(0x00000000);
-        SkPaint darkPaint;
-        darkPaint.setColor(0xFF404040);
-        SkPaint lightPaint;
-        lightPaint.setColor(0xFFA0A0A0);
-        for (int y = 0; y < 64; y += 16) {
-          for (int x = 0; x < 64; x += 16) {
-            canvas.save();
-            canvas.translate(SkIntToScalar(x), SkIntToScalar(y));
-            canvas.drawRect(SkRect::MakeXYWH(0, 0, 8, 8), darkPaint);
-            canvas.drawRect(SkRect::MakeXYWH(8, 0, 8, 8), lightPaint);
-            canvas.drawRect(SkRect::MakeXYWH(0, 8, 8, 8), lightPaint);
-            canvas.drawRect(SkRect::MakeXYWH(8, 8, 8, 8), darkPaint);
-            canvas.restore();
-          }
-        }
-    }
-
     void make_gradient_circle(int width, int height) {
         SkScalar x = SkIntToScalar(width / 2);
         SkScalar y = SkIntToScalar(height / 2);
@@ -82,7 +62,10 @@ protected:
 
     void onDraw(SkCanvas* canvas) SK_OVERRIDE {
         if (!fInitialized) {
-            this->make_checkerboard();
+            fCheckerboard.allocN32Pixels(64, 64);
+            SkCanvas checkerboardCanvas(fCheckerboard);
+            sk_tools::DrawCheckerboard(&checkerboardCanvas, 0xFFA0A0A0, 0xFF404040, 8);
+
             this->make_gradient_circle(64, 64);
             fInitialized = true;
         }
diff --git a/gm/imagefiltersscaled.cpp b/gm/imagefiltersscaled.cpp
index b419187fff..084de00fbe 100644
--- a/gm/imagefiltersscaled.cpp
+++ b/gm/imagefiltersscaled.cpp
@@ -5,20 +5,21 @@
  * found in the LICENSE file.
  */
 
-#include "gm.h"
-#include "SkColor.h"
+#include "Checkerboard.h"
 #include "SkBitmapSource.h"
 #include "SkBlurImageFilter.h"
+#include "SkColor.h"
 #include "SkDisplacementMapEffect.h"
 #include "SkDropShadowImageFilter.h"
 #include "SkGradientShader.h"
 #include "SkLightingImageFilter.h"
+#include "SkMatrixImageFilter.h"
 #include "SkMorphologyImageFilter.h"
 #include "SkOffsetImageFilter.h"
 #include "SkPerlinNoiseShader.h"
 #include "SkRectShaderImageFilter.h"
-#include "SkMatrixImageFilter.h"
 #include "SkScalar.h"
+#include "gm.h"
 
 #define RESIZE_FACTOR SkIntToScalar(4)
 
@@ -40,27 +41,6 @@ protected:
         return SkISize::Make(1428, 500);
     }
 
-    void make_checkerboard() {
-        fCheckerboard.allocN32Pixels(64, 64);
-        SkCanvas canvas(fCheckerboard);
-        canvas.clear(0x00000000);
-        SkPaint darkPaint;
-        darkPaint.setColor(0xFF404040);
-        SkPaint lightPaint;
-        lightPaint.setColor(0xFFA0A0A0);
-        for (int y = 0; y < 64; y += 16) {
-          for (int x = 0; x < 64; x += 16) {
-            canvas.save();
-            canvas.translate(SkIntToScalar(x), SkIntToScalar(y));
-            canvas.drawRect(SkRect::MakeXYWH(0, 0, 8, 8), darkPaint);
-            canvas.drawRect(SkRect::MakeXYWH(8, 0, 8, 8), lightPaint);
-            canvas.drawRect(SkRect::MakeXYWH(0, 8, 8, 8), lightPaint);
-            canvas.drawRect(SkRect::MakeXYWH(8, 8, 8, 8), darkPaint);
-            canvas.restore();
-          }
-        }
-    }
-
     void make_gradient_circle(int width, int height) {
         SkScalar x = SkIntToScalar(width / 2);
         SkScalar y = SkIntToScalar(height / 2);
@@ -82,7 +62,10 @@ protected:
 
     virtual void onDraw(SkCanvas* canvas) {
         if (!fInitialized) {
-            this->make_checkerboard();
+            fCheckerboard.allocN32Pixels(64, 64);
+            SkCanvas checkerboardCanvas(fCheckerboard);
+            sk_tools::DrawCheckerboard(&checkerboardCanvas, 0xFFA0A0A0, 0xFF404040, 8);
+
             this->make_gradient_circle(64, 64);
             fInitialized = true;
         }
diff --git a/gm/offsetimagefilter.cpp b/gm/offsetimagefilter.cpp
index 3dafed8823..2e80a96e34 100644
--- a/gm/offsetimagefilter.cpp
+++ b/gm/offsetimagefilter.cpp
@@ -5,9 +5,10 @@
  * found in the LICENSE file.
  */
 
-#include "gm.h"
-#include "SkOffsetImageFilter.h"
+#include "Checkerboard.h"
 #include "SkBitmapSource.h"
+#include "SkOffsetImageFilter.h"
+#include "gm.h"
 
 #define WIDTH 600
 #define HEIGHT 100
@@ -39,27 +40,6 @@ protected:
         canvas.drawText(str, strlen(str), SkIntToScalar(15), SkIntToScalar(65), paint);
     }
 
-    void make_checkerboard() {
-        fCheckerboard.allocN32Pixels(80, 80);
-        SkCanvas canvas(fCheckerboard);
-        canvas.clear(0x00000000);
-        SkPaint darkPaint;
-        darkPaint.setColor(0xFF404040);
-        SkPaint lightPaint;
-        lightPaint.setColor(0xFFA0A0A0);
-        for (int y = 0; y < 80; y += 16) {
-          for (int x = 0; x < 80; x += 16) {
-            canvas.save();
-            canvas.translate(SkIntToScalar(x), SkIntToScalar(y));
-            canvas.drawRect(SkRect::MakeXYWH(0, 0, 8, 8), darkPaint);
-            canvas.drawRect(SkRect::MakeXYWH(8, 0, 8, 8), lightPaint);
-            canvas.drawRect(SkRect::MakeXYWH(0, 8, 8, 8), lightPaint);
-            canvas.drawRect(SkRect::MakeXYWH(8, 8, 8, 8), darkPaint);
-            canvas.restore();
-          }
-        }
-    }
-
     virtual SkISize onISize() {
         return SkISize::Make(WIDTH, HEIGHT);
     }
@@ -90,7 +70,11 @@ protected:
     virtual void onDraw(SkCanvas* canvas) {
         if (!fInitialized) {
             make_bitmap();
-            make_checkerboard();
+
+            fCheckerboard.allocN32Pixels(80, 80);
+            SkCanvas checkerboardCanvas(fCheckerboard);
+            sk_tools::DrawCheckerboard(&checkerboardCanvas, 0xFFA0A0A0, 0xFF404040, 8);
+
             fInitialized = true;
         }
         canvas->clear(0x00000000);
diff --git a/gm/tileimagefilter.cpp b/gm/tileimagefilter.cpp
index 7d1a3f08c3..1d58def66b 100644
--- a/gm/tileimagefilter.cpp
+++ b/gm/tileimagefilter.cpp
@@ -5,11 +5,12 @@
  * found in the LICENSE file.
  */
 
-#include "gm.h"
-#include "SkColorMatrixFilter.h"
+#include "Checkerboard.h"
+#include "SkBitmapSource.h"
 #include "SkColorFilterImageFilter.h"
+#include "SkColorMatrixFilter.h"
 #include "SkTileImageFilter.h"
-#include "SkBitmapSource.h"
+#include "gm.h"
 
 #define WIDTH 400
 #define HEIGHT 100
@@ -41,27 +42,6 @@ protected:
         canvas.drawText(str, strlen(str), SkIntToScalar(10), SkIntToScalar(45), paint);
     }
 
-    void make_checkerboard() {
-        fCheckerboard.allocN32Pixels(80, 80);
-        SkCanvas canvas(fCheckerboard);
-        canvas.clear(0x00000000);
-        SkPaint darkPaint;
-        darkPaint.setColor(0xFF404040);
-        SkPaint lightPaint;
-        lightPaint.setColor(0xFFA0A0A0);
-        for (int y = 0; y < 80; y += 16) {
-          for (int x = 0; x < 80; x += 16) {
-            canvas.save();
-            canvas.translate(SkIntToScalar(x), SkIntToScalar(y));
-            canvas.drawRect(SkRect::MakeXYWH(0, 0, 8, 8), darkPaint);
-            canvas.drawRect(SkRect::MakeXYWH(8, 0, 8, 8), lightPaint);
-            canvas.drawRect(SkRect::MakeXYWH(0, 8, 8, 8), lightPaint);
-            canvas.drawRect(SkRect::MakeXYWH(8, 8, 8, 8), darkPaint);
-            canvas.restore();
-          }
-        }
-    }
-
     virtual SkISize onISize() {
         return SkISize::Make(WIDTH, HEIGHT);
     }
@@ -69,7 +49,11 @@ protected:
     virtual void onDraw(SkCanvas* canvas) {
         if (!fInitialized) {
             make_bitmap();
-            make_checkerboard();
+
+            fCheckerboard.allocN32Pixels(80, 80);
+            SkCanvas checkerboardCanvas(fCheckerboard);
+            sk_tools::DrawCheckerboard(&checkerboardCanvas, 0xFFA0A0A0, 0xFF404040, 8);
+
             fInitialized = true;
         }
         canvas->clear(0x00000000);
diff --git a/gm/xfermodeimagefilter.cpp b/gm/xfermodeimagefilter.cpp
index ac5fa5e4b2..b90543ffb4 100644
--- a/gm/xfermodeimagefilter.cpp
+++ b/gm/xfermodeimagefilter.cpp
@@ -6,6 +6,7 @@
  */
 
 #include "gm.h"
+#include "Checkerboard.h"
 #include "SkArithmeticMode.h"
 #include "SkOffsetImageFilter.h"
 #include "SkXfermodeImageFilter.h"
@@ -41,27 +42,6 @@ protected:
         canvas.drawText(str, strlen(str), SkIntToScalar(15), SkIntToScalar(65), paint);
     }
 
-    void make_checkerboard() {
-        fCheckerboard.allocN32Pixels(80, 80);
-        SkCanvas canvas(fCheckerboard);
-        canvas.clear(0x00000000);
-        SkPaint darkPaint;
-        darkPaint.setColor(0xFF404040);
-        SkPaint lightPaint;
-        lightPaint.setColor(0xFFA0A0A0);
-        for (int y = 0; y < 80; y += 16) {
-          for (int x = 0; x < 80; x += 16) {
-            canvas.save();
-            canvas.translate(SkIntToScalar(x), SkIntToScalar(y));
-            canvas.drawRect(SkRect::MakeXYWH(0, 0, 8, 8), darkPaint);
-            canvas.drawRect(SkRect::MakeXYWH(8, 0, 8, 8), lightPaint);
-            canvas.drawRect(SkRect::MakeXYWH(0, 8, 8, 8), lightPaint);
-            canvas.drawRect(SkRect::MakeXYWH(8, 8, 8, 8), darkPaint);
-            canvas.restore();
-          }
-        }
-    }
-
     SkISize onISize() SK_OVERRIDE {
         return SkISize::Make(WIDTH, HEIGHT);
     }
@@ -87,7 +67,10 @@ protected:
 
     void onOnceBeforeDraw() SK_OVERRIDE {
         make_bitmap();
-        make_checkerboard();
+
+        fCheckerboard.allocN32Pixels(80, 80);
+        SkCanvas checkerboardCanvas(fCheckerboard);
+        sk_tools::DrawCheckerboard(&checkerboardCanvas, 0xFFA0A0A0, 0xFF404040, 8);
     }
 
     void onDraw(SkCanvas* canvas) SK_OVERRIDE {
diff --git a/gyp/SampleApp.gyp b/gyp/SampleApp.gyp
index 7767835437..f961f1182b 100644
--- a/gyp/SampleApp.gyp
+++ b/gyp/SampleApp.gyp
@@ -152,6 +152,7 @@
         'skia_lib.gyp:skia_lib',
         'tools.gyp:resources',
         'tools.gyp:sk_tool_utils',
+        'tools.gyp:checkerboard',
         'views.gyp:views',
         'views_animated.gyp:views_animated',
         'xml.gyp:xml',
diff --git a/gyp/gmslides.gypi b/gyp/gmslides.gypi
index abcb86767b..e716644750 100644
--- a/gyp/gmslides.gypi
+++ b/gyp/gmslides.gypi
@@ -7,6 +7,9 @@
     '../src/images',
     '../src/lazy',
   ],
+  'dependencies': [
+     'tools.gyp:checkerboard',
+  ],
   'conditions': [
     # If we're building SampleApp on the bots, no need to link in the GM slides.
     # We're not going to run it; we're only making sure it still builds.
diff --git a/gyp/tools.gyp b/gyp/tools.gyp
index 1b196a75b1..8d2c7037b1 100644
--- a/gyp/tools.gyp
+++ b/gyp/tools.gyp
@@ -89,6 +89,13 @@
       },
     },
     {
+      'target_name': 'checkerboard',
+      'type': 'static_library',
+      'sources': [ '../tools/Checkerboard.cpp', ],
+      'dependencies': [ 'skia_lib.gyp:skia_lib', ],
+      'direct_dependent_settings': { 'include_dirs': [ '../tools', ], },
+    },
+    {
       'target_name' : 'timer',
       'type': 'static_library',
       'sources': [
diff --git a/samplecode/SampleColorFilter.cpp b/samplecode/SampleColorFilter.cpp
index fb5d42744f..175f724710 100644
--- a/samplecode/SampleColorFilter.cpp
+++ b/samplecode/SampleColorFilter.cpp
@@ -5,6 +5,7 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
+#include "Checkerboard.h"
 #include "SampleCode.h"
 #include "SkView.h"
 #include "SkCanvas.h"
@@ -84,20 +85,6 @@ static void test_5bits() {
     SkDebugf("--- trunc: %d %d  round: %d %d new: %d %d\n", e0, ae0, e1, ae1, e2, ae2);
 }
 
-// No longer marked static, since it is externed in SampleUnpremul.
-SkShader* createChecker();
-SkShader* createChecker() {
-    SkBitmap bm;
-    bm.allocN32Pixels(2, 2);
-    bm.lockPixels();
-    *bm.getAddr32(0, 0) = *bm.getAddr32(1, 1) = SkPreMultiplyColor(0xFFFFFFFF);
-    *bm.getAddr32(0, 1) = *bm.getAddr32(1, 0) = SkPreMultiplyColor(0xFFCCCCCC);
-    SkMatrix m;
-    m.setScale(12, 12);
-    return SkShader::CreateBitmapShader(bm, SkShader::kRepeat_TileMode,
-                                        SkShader::kRepeat_TileMode, &m);
-}
-
 static SkBitmap createBitmap(int n) {
     SkBitmap bitmap;
     bitmap.allocN32Pixels(n, n);
@@ -131,7 +118,8 @@ class ColorFilterView : public SampleView {
 public:
     ColorFilterView() {
         fBitmap = createBitmap(N);
-        fShader = createChecker();
+        fShader = sk_tools::CreateCheckerboardShader(
+                0xFFCCCCCC, 0xFFFFFFFF, 12);
 
         if (false) { // avoid bit rot, suppress warning
             test_5bits();
diff --git a/samplecode/SampleFatBits.cpp b/samplecode/SampleFatBits.cpp
index 9b9af3e3e9..9da351370a 100644
--- a/samplecode/SampleFatBits.cpp
+++ b/samplecode/SampleFatBits.cpp
@@ -5,6 +5,7 @@
  * found in the LICENSE file.
  */
 
+#include "Checkerboard.h"
 #include "SampleCode.h"
 #include "SkView.h"
 #include "SkCanvas.h"
@@ -35,18 +36,6 @@ static void erase(SkSurface* surface) {
     surface->getCanvas()->clear(SK_ColorTRANSPARENT);
 }
 
-static SkShader* createChecker(const SkMatrix& localMatrix) {
-//    SkColor colors[] = { 0xFFFDFDFD, 0xFFF4F4F4 };
-    SkColor colors[] = { 0xFFFFFFFF, 0xFFFFFFFF };
-    SkBitmap bm;
-    bm.allocN32Pixels(2, 2);
-    bm.lockPixels();
-    *bm.getAddr32(0, 0) = *bm.getAddr32(1, 1) = SkPreMultiplyColor(colors[0]);
-    *bm.getAddr32(0, 1) = *bm.getAddr32(1, 0) = SkPreMultiplyColor(colors[1]);
-    return SkShader::CreateBitmapShader(bm, SkShader::kRepeat_TileMode,
-                                        SkShader::kRepeat_TileMode, &localMatrix);
-}
-
 class FatBits {
 public:
     FatBits() {
@@ -98,7 +87,8 @@ public:
         fBounds.set(0, 0, SkIntToScalar(width * zoom), SkIntToScalar(height * zoom));
         fMatrix.setScale(SkIntToScalar(zoom), SkIntToScalar(zoom));
         fInverse.setScale(SK_Scalar1 / zoom, SK_Scalar1 / zoom);
-        fShader.reset(createChecker(fMatrix));
+        fShader.reset(sk_tools::CreateCheckerboardShader(
+                              0xFFCCCCCC, 0xFFFFFFFF, zoom));
 
         SkImageInfo info = SkImageInfo::MakeN32Premul(width, height);
         fMinSurface.reset(SkSurface::NewRaster(info));
diff --git a/samplecode/SampleUnpremul.cpp b/samplecode/SampleUnpremul.cpp
index 9591fec159..889d06780e 100644
--- a/samplecode/SampleUnpremul.cpp
+++ b/samplecode/SampleUnpremul.cpp
@@ -7,6 +7,7 @@
 
 #include "gm.h"
 
+#include "Checkerboard.h"
 #include "Resources.h"
 #include "SampleCode.h"
 #include "SkBlurMask.h"
@@ -25,9 +26,6 @@
 
 __SK_FORCE_IMAGE_DECODER_LINKING;
 
-// Defined in SampleColorFilter.cpp
-extern SkShader* createChecker();
-
 /**
  *  Interprets c as an unpremultiplied color, and returns the
  *  premultiplied equivalent.
@@ -78,10 +76,7 @@ protected:
     }
 
     void onDrawBackground(SkCanvas* canvas) SK_OVERRIDE {
-        SkPaint paint;
-        SkAutoTUnref<SkShader> shader(createChecker());
-        paint.setShader(shader.get());
-        canvas->drawPaint(paint);
+        sk_tools::DrawCheckerboard(canvas, 0xFFCCCCCC, 0xFFFFFFFF, 12);
     }
 
     void onDrawContent(SkCanvas* canvas) SK_OVERRIDE {
diff --git a/tools/Checkerboard.cpp b/tools/Checkerboard.cpp
new file mode 100644
index 0000000000..80de125f15
--- /dev/null
+++ b/tools/Checkerboard.cpp
@@ -0,0 +1,28 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "Checkerboard.h"
+#include "SkCanvas.h"
+#include "SkShader.h"
+
+SkShader* sk_tools::CreateCheckerboardShader(
+        SkColor c1, SkColor c2, int size) {
+    SkBitmap bm;
+    bm.allocN32Pixels(2 * size, 2 * size);
+    bm.eraseColor(c1);
+    bm.eraseArea(SkIRect::MakeLTRB(0, 0, size, size), c2);
+    bm.eraseArea(SkIRect::MakeLTRB(size, size, 2 * size, 2 * size), c2);
+    return SkShader::CreateBitmapShader(
+            bm, SkShader::kRepeat_TileMode, SkShader::kRepeat_TileMode);
+}
+
+void sk_tools::DrawCheckerboard(SkCanvas* canvas,
+                                    SkColor c1, SkColor c2, int size) {
+    SkPaint paint;
+    paint.setShader(CreateCheckerboardShader(c1, c2, size))->unref();
+    canvas->drawPaint(paint);
+}
diff --git a/tools/Checkerboard.h b/tools/Checkerboard.h
new file mode 100644
index 0000000000..b81e43616f
--- /dev/null
+++ b/tools/Checkerboard.h
@@ -0,0 +1,34 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#ifndef Checkerboard_DEFINED
+#define Checkerboard_DEFINED
+
+#include "SkColor.h"
+
+class SkCanvas;
+class SkShader;
+
+namespace sk_tools {
+
+/** Returns a newly created CheckerboardShader. */
+SkShader* CreateCheckerboardShader(SkColor c1, SkColor c2, int size);
+
+/** Draw a checkerboard pattern in the current canvas, restricted to
+    the current clip. */
+void DrawCheckerboard(SkCanvas* canvas,
+                      SkColor color1,
+                      SkColor color2,
+                      int size);
+
+/** A default checkerboard. */
+inline void DrawCheckerboard(SkCanvas* canvas) {
+    sk_tools::DrawCheckerboard(canvas, 0xFF999999, 0xFF666666, 8);
+}
+
+}  // namespace sk_tools
+
+#endif  // Checkerboard_DEFINED